To the unscientific mind the slides are terrifying in their magnitude and in the evidence they give of irresistible force. Man can no more check their advance than he can that of a glacier which in a way they resemble. When I was on the Isthmus the great Cucaracha slide was in progress, and had been for that matter since 1907. It had a total area of 47 acres and extended up the east bank of the Canal for about 1900 feet from the axis of the Canal. When it began its progress was disconcertingly rapid. Its base, foot, or “toe”--these anatomical terms in engineering are sometimes perplexing--moved across the canal bed at the rate of 14 feet a day. All that stood in its path was buried, torn to pieces or carried along with the resistless glacier of mud. Not content with filling the Canal from one side to the other, the dirt rose on the further side to a height of about 30 feet. Not only was the work of months obliterated, but work was laid out for years to come. Indeed in 1913 they were still digging at the Cucaracha slide and the end was not in sight. This slide was wholly a gravity slide, caused by a mass of earth slipping on the inclined surface of some smooth and slippery material like clay on which it rests. The nature of the phenomenon is clearly shown by the diagram printed on the next page in which the slide marked C is of the type just described. [Illustration: ATTACKING THE CUCARACHA SLIDE This slide has filled the Cut from side to side. A partial Cut has been dug through its center and the shovels are seen working on either side. The tracks are moved nightly as the material is removed.]